Brake shoe retainer clip

ABSTRACT

A retaining clip is used to maintain proper shoe contact and orientation for a cam actuated brake assembly. The brake assembly includes a pair of brake shoes each having an anchor end and an actuation end. Each brake shoe is pivotally mounted at the anchor end to a brake spider with an anchor pin. When the brakes are applied, a cam acts against the actuation end causing the brake shoes to pivot about axes defined by the anchor pins. Preferably the retaining clip is mounted to the brake shoe and includes a pair of hooks that support opposite ends of the anchor pin. The retaining clip cooperates with the anchor pins to maintain proper shoe geometry.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a retainer clip for a brake shoe thathelps to maintain proper shoe geometry. Specifically, retaining clipsare mounted to each brake shoe to interact with the anchor pins formaintaining shoe contact, proper shoe orientation, and prevent shoe dragwhen the brake assembly is not applied.

[0002] Drum brakes are widely used in vehicle braking systems. In atypical drum brake, two arcuate brake shoe assemblies are located insidea rotating cylindrical brake drum. Each brake shoe assembly includes abacking plate that carries brake lining friction material. A brakeactuator moves the brake shoe assemblies toward the rotating brake drumsuch that the brake lining friction material contacts the inner surfacesof the drum, thus retarding the rotation of the drum.

[0003] The brake shoe assemblies are mounted to a central plate or brakespider. At one end each brake shoe is pivotally supported on an anchorpin. At the opposite end of each brake shoe, the brake actuator(typically a cam) applies an actuation force against the shoes causingthe shoes to pivot about axes define by the anchor pins. The actuatorcauses the brake shoes to pivot away from each other toward the rotatingbrake drum. Return springs are used to return the brake shoes after eachbrake actuation. The brake assembly also includes a pair of retainersprings for each brake shoe mounted on the anchor pin end. The retainersprings maintain the shoe contact and orientation with the anchor pinand prevent the shoe from dragging when the brake is not applied.

[0004] In some instances, depending on the braking application, theretainer springs lack sufficient strength and fatigue life. In thesecircumstances, a heavier duty brake including a full web around theanchor pin is required, which increases cost.

[0005] Further, the retaining springs are an extension spring type thatis designed such that in the installed condition the spring is in aslight extension that results in a sufficient load to retain the weightof the shoe relative to the anchor pin. The spring includes a collectionof closed coils with either hooks formed on the ends of the coils orhook details attached to the ends of the coils.

[0006] There are several disadvantages to using an extension springdesign. Coil clashing and stress concentrations can lead to earlyfailure. Coil clashing is caused by the closed coil design where coilscollide as a result of normal road vibration, which can result infatigue failure. Another disadvantage is caused by the springmanufacturing process. This process typically includes coiling springwire over a mandrel, which introduces a tool mark on the spring. Thesmall diameter of the spring and the close coil design do not permitprocess enhancements, such as shot peening, resulting in a stressconcentration in the already highly stressed inner coil area. Also,crimping hooks onto the ends of the spring introduces additional toolmarks that result in stress concentrations.

[0007] Thus, it is desirable to have a brake retaining mechanism thatdoes not require extension springs. The brake retaining mechanism shouldbe robust and be able to be used in multiple brake show configurationsin addition to overcoming the above referenced deficiencies with priorart systems.

SUMMARY OF THE INVENTION

[0008] The subject invention includes a retaining clip that is used tomaintain proper shoe contact and orientation for a cam actuated brakeassembly. The retaining clip eliminates the need for retaining springscurrently used in the brake assembly to maintain proper shoe geometry.The retaining clip is mounted to a brake shoe and cooperates with abrake shoe anchor pin to consistently achieve the correct orientation.

[0009] In a disclosed embodiment, the brake assembly includes a pair ofbrake shoes having backing plates for supporting brake linings foractuation by a cam against a rotating drum. Each brake shoe has ananchor end and an actuation end. Each brake shoe is pivotally mounted atthe anchor end to a brake spider with an anchor pin. When the brakes areapplied, the cam acts against the actuation end causing the brake shoesto pivot away from one another about axes defined by the anchor pins.

[0010] In the preferred embodiment, the retaining clip is mounted to thebacking plate of the brake shoe. The retaining clip includes a baseplate with a pair of transversely extending legs that support oppositeends of the anchor pin. The base plate preferably includes a resilienttab portion that grips a portion of the backing plate. The anchor pinincludes a cylindrical body having a pair of pin ends of smallerdiameter than the body extending outwardly from opposing sides of thebody. The legs of the retaining clip preferably have hooked ends forengaging the pin ends. The hooked ends cooperate with the pin ends tomaintain proper shoe geometry.

[0011] The subject invention provides a brake shoe retaining clip thateliminates the need for retaining springs. The retaining clip provides amore robust design and has increased fatigue life over prior artsystems. These and other features of the present invention can be bestunderstood from the following specification and drawings, the followingof which is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic representation of a cam brake assemblyincorporation the subject invention.

[0013]FIG. 2 is an exploded view of a prior art cam brake system.

[0014]FIG. 3 is an exploded view, partially cut-away, of one embodimentof the subject invention.

[0015]FIG. 4 is a side view of an alternate embodiment of the subjectinvention.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

[0016] Referring to FIG. 1, a brake shoe assembly having a retainingclip in accordance with the present invention is shown installed in avehicular brake system.

[0017]FIG. 1 is a side view of a drum brake system 10. The drum brakesystem 10 includes a cylindrical brake drum 12, a first brake shoeassembly generally shown at 14, a second brake shoe assembly generallyshown at 16, and an actuator 18. The general operation of the brake drumassembly 10 is known. The first and second brake shoe assemblies 14 and16 are preferably identical such that a description of the first brakeshoe assembly 14 or its components is also applicable to the secondbrake shoe assembly 16. The actuator 18, shown schematically in FIG. 1,is an s-cam mechanism that is rotated during a brake actuation causingthe brake shoes 14, 16 to engage the drum 12.

[0018] The brake drum 12, which rotates about an axis of rotation 20,has an inner surface 22 and an outer surface 24. The first and secondbrake shoe assemblies 14 and 16, located adjacent to the inner surface22 of the brake drum 12, include a brake lining 26 having apredetermined thickness. The brake linings 26 are comprised of a knownfriction material attached to a backing plate 28. Each brake lining 26presents a wear surface 32, which contacts the inner surface 22 of therotating brake drum 12 and wears further and further away each time theactuator 18 moves the first and second brake shoe assemblies 14 and 16against the brake drum 12.

[0019] Each brake shoe 14, 16 is pivotally mounted at one end 34 to abrake spider 36 with an anchor pin 38. The anchor pin ends 34 of thebrake shoes 14, 16 are opposite from actuation ends 40 of the brakeshoes 14, 16. The anchor pin 38 for the first brake shoe 14 defines afirst pivot axis 42 and the anchor pin 38 for the second brake shoe 16defines a second pivot axis 44. When the brakes are applied, theactuator 18 pivots the shoes 14, 16 about the first 42 and second 44pivot axes, respectively.

[0020] A prior art cam brake assembly is shown in FIG. 2. This assemblyincludes a return spring 46 that returns the brake shoes 14, 16 to theiroriginal position after each brake actuation. The brake assembly alsoincludes a pair of retainer springs 48 (only one set is shown) for eachbrake shoe 14, 16 mounted on the anchor pin end. The retainer springs 48maintain the shoe contact and orientation with the anchor pin 38 andprevent the shoes 14, 16 from dragging when the brake is not applied.

[0021] These retaining springs 48 are extension springs that aredesigned such that in the installed condition the spring is in a slightextension that results in a sufficient load to retain the weight of theshoe relative to the anchor pin 38. The use of this type of spring isdisadvantageous and can lead to early failure. Coil clashing caused bynormal road vibration can result in early fatigue failure. The springmanufacturing process can introduce a tool marks on the spring resultingstress concentrations, which can lead to premature failure.

[0022] Thus, the subject invention includes a retainer clip 50, shown inFIG. 3, which eliminates the need for retaining springs 48. Theretaining clip 50 preferably includes a base portion 52 with a pair oftransversely extending legs 54 positioned on opposite sides of the baseportion 52. Each leg 54 preferably has a hooked end 56 that engages theanchor pin 38. It should be understood that there is one retaining clip50 for each brake shoe 14, 16. Thus, the retaining clip 50 shown in FIG.3 is the same for each brake shoe 14, 16.

[0023] The anchor pin 38 includes a cylindrical body 58 and a pair ofpin ends 60 positioned on opposite sides of the body 58 to define thepivot axis 42. The pin ends 60 have a significantly smaller diameterthan the body 58. The hooked ends 56 of the clip 50 engage the pin ends60 to maintain the proper shoe geometry.

[0024] The clip 50 can be attached to any portion of the brake shoe 14with any known attachment method, however, in the preferred embodimentthe clip 50 is mounted to the backing plate 28 with a resilient tab 62.The tab 62 includes at least one grip 64 to engage the backing plate 28.Preferably the grip 64 is a pointed tooth member that clips onto theplate 28 such that the tab 62 is on one side of the plate 28 with theremaining portions of the base 52 being positioned on the opposite sideof the plate 28.

[0025] The clip 50 can be attached to the plate 28, as shown in FIG. 3,or can be attached to another portion of the shoe 14, as shown in FIG.4. Each brake shoe 14 includes a pair of transversely extending webbedflanges 70 that extend inwardly toward the center of the brake assembly.The webbed flanges 70 define an engagement surface 72 that receives aportion of the body 58 of the anchor pin 28. In the alternate embodimentof FIG. 4, the clip 50 is shown attached to the flanges 70. The clip 50can be attached to one or both of the flanges 70.

[0026] When the cam 18 is applied, the shoes 14, 16, the clips 50, andthe anchor pins 38 pivot as a unit about their respective axes 42, 44.The return spring 46 is used to return the shoes 14, 16 to theiroriginal position and the retaining clips 50 cooperate with the anchorpins 38 to maintain proper shoe contact and orientation.

[0027] The subject invention provides a brake shoe retaining clip 50that eliminates the need for retaining springs 48. The retaining clip 50provides a more robust design and has increased fatigue life over priorart systems.

[0028] Although a preferred embodiment of this invention has beendisclosed, it should be understood that a worker of ordinary skill inthe art would recognize many modifications come within the scope of thisinvention. For that reason, the following claims should be studied todetermine the true scope and content of this invention.

I claim:
 1. A brake shoe assembly comprising: a brake spider; a mountingmember supported on said brake spider and including an arcuate surfacefor supporting a brake lining; an anchor pin pivotally mounting one endof said mounting member to said brake spider; and a retainer clipattached to said mounting member and cooperating with said anchor pin tomaintain proper shoe orientation.
 2. An assembly according to claim 1wherein said retainer clip includes a base member with a connectorportion and a pair of legs extending outwardly from opposite ends ofsaid base member to support said anchor pin.
 3. An assembly according toclaim 2 wherein said anchor pin includes a cylindrical body with a pairof pin ends extending in opposite directions form said body to define apivot axis and wherein said pin ends are supported by said legs.
 4. Anassembly according to claim 3 wherein said retainer clip, said anchorpin, and said mounting member all rotated about said pivot axis duringbrake actuation.
 5. An assembly according to claim 3 wherein saidmounting member includes a base plate for supporting said brake liningand a pair of spaced apart webbed flanges extending inwardly from saidbase plate toward said pivot axis, said connector portion engaging saidbase plate between said flanges to retain said clip on said mountingmember.
 6. An assembly according to claim 5 wherein said connectorportion includes a resiliently biased tab with at least one transverselyextending grip for engaging said base plate.
 7. An assembly according toclaim 3 wherein said mounting member includes a base plate forsupporting said brake lining and a pair of spaced apart webbed flangesextending inwardly from said base plate toward the center of theassembly, said connector portion engaging at least one of said webbedflanges to retain said clip on said mounting member.
 8. An assemblyaccording to claim 3 wherein said legs have a hook portion forsupporting said pin ends.
 9. A cam brake assembly comprising: a firstbrake shoe including a first backing plate for supporting a first brakelining; a second brake shoe including a second backing plate forsupporting a second brake lining wherein said second brake lining facesan opposite direction from said first brake lining; a brake spiderhaving a first mounting portion for attachment to said first brake shoeand a second mounting portion for attachment to said second brake shoe;a first anchor pin pivotally attaching one end of said first brake shoeto said first mounting portion to define a first pivot axis; a secondanchor pin pivotally attaching one end of said second brake shoe to saidsecond mounting portion to define a second pivot axis; an actuator forpivoting opposite ends of said first and second brake shoes about saidfirst and second pivot axes, respectively, during a brake actuation; afirst retainer clip attached to said first brake shoe for cooperationwith said first anchor pin to maintain proper contact and orientationbetween said first anchor pin and said first brake shoe; and a secondretainer clip attached to said second brake shoe for cooperation withsaid second anchor pin to maintain proper contract and orientationbetween said second anchor pin and said second brake shoe.
 10. Anassembly according to claim 9 wherein said first retainer clip isattached to said first backing plate and said second retainer clip isattached to said second backing plate.
 11. An assembly according toclaim 9 wherein each of said backing plates include a pair of spacedapart transversely extending webbed flanges each defining an engagementsurface for contact with said anchor pin.
 12. An assembly according toclaim 11 wherein said first and second retainer clips are attached tosaid webbed flanges of said first and second backing plates.
 13. Anassembly according to claim 11 wherein each of said anchor pins includea cylindrical body and a pair of pin ends of smaller diameter than saidbody extending outwardly from opposing ends of said body and wherein anexterior surface of said body contacts said engagement surfaces of saidwebbed flanges.
 14. An assembly according to claim 13 wherein each ofsaid retainer clips include a base plate with a pair of hooked legs forsupporting said pin ends.
 15. An assembly according to claim 11 whereinsaid first retainer clip, said first brake shoe, and said first anchorpin all pivot about said first pivot axis during a brake actuation andsaid second retainer clip, said second brake shoe, and said secondanchor pin all pivot about said second pivot axis during a brakeactuation.
 16. An assembly according to claim 9 wherein each of saidretainer clips include a connector portion having a resilient tab withat least one grip for engaging a portion of said brake shoes to retainsaid clips to said shoes.